Battery systems (e.g., including one or more batteries) are becoming more and more important in everyday life since the spectrum of applications have been widely broadened, ranging from portable devices such as cell phones to heavier duty applications such as fork lifts, golf carts, and even electric or hybrid electric vehicles in recent years. In any of the applications mentioned above (or other applications), reliable state of charge monitoring is important in enabling battery systems to be commercially viable. In some cases, such as electric and hybrid vehicles, the state of charge monitoring may even be related to safety issues.